A method for producing micromechanical sensors is discussed in German patent document DE 101 14 036 A1. There, openings, which transform themselves into cavities in the depth of the substrate under a sealed diaphragm cover during a subsequent heat treatment, are introduced in a semiconductor substrate. A capacitive pressure sensor can be produced by this method, the cavity being created between two doping zones in the substrate. If these two zones are electrically insulated from one another they form a plate-type capacitor whose capacitance depends on the spacing of the doping zones. Both doping zones can be electrically connected to a suitable evaluation circuit by deep contacting. A deformation of the semiconductor substrate can thus be converted into a measurable change in the capacitance. The measuring result results as ratio of the ambient pressure relative to the pressure inside the cavity. The sensor element described in the document has the disadvantage that the two electrodes are insulated from one another only via pn transitions, which constitute parasitic capacitances and lead to undesired leakage currents.
Another method for producing a cavity in a semiconductor substrate is discussed in the not pre-published patent document DE 10 2004 04 3357 A1. In this case, a lattice-like structure made from a substrate material etched non-porous is created on the surface of a semiconductor substrate. A porosified region is produced into the depth of the semiconductor substrate between the lattice-like structure. With the aid of a subsequent heat treatment, the porosified region is then transformed into a cavity by relocation of the semiconductor material. At the same time, the heat treatment may also be used to reform the lattice-like structure into a diaphragm above the cavity.
The production of a diaphragm with the aid of an epitaxy layer on stabilizing elements above a cavity is discussed in the not pre-published patent document DE 10 2004 03 6032 A1. In this case, material is selectively dissolved out of the semiconductor material to form the stabilizing elements, thereby creating porous silicon in the porous region that later includes the cavity.
The design of a capacitive micromechanical sensor element with the aid of different epitaxy layers is discussed in the not pre-published patent document DE 10 2004 06 1796 A1.